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Published byVance Witherell Modified about 1 year ago

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Chapter 5 Operational Amplifier

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Introduction A typical op amp: a) pin configuration, b) circuit symbol An op amp is an active circuit element designed to perform mathematical operation of addition, subtraction, multiplication, division, differentiation, and integration.

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Terminal Voltage and Currents Vd=V2-V1 (differencial input) Vo=AVd=A(V2-V1) A: gain (open-loop voltage gain)

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Actual op amp: Ri(very large); Ro(very small); A(very large) Idealization: Ri=> ; Ro=>0 ; A=> As Vo is limited, we can get from Vo=A(V2-V1) that: V2=V1 As Ri=> , we can get i 1 =0, i 2 =0 i1i1 i2i2

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Ideal op amp 1)i1=0, i2=0 ; 2)V1=V2 Ideal op amp model i1 i2

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Applications Inverting Amplifier

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Applications Noninverting amplifier If Rf=0; R1= , then=>

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The voltage follower ViVi VoVo First stage Second stage Applications

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Summing amplifier

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Difference Amplifier Note: be careful while using nodal analysis, do not set nodal equation at the output terminal.

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Example: Find out Vo

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P.P.5.10As a voltage follower, v a = v 1 = 2V where v a is the voltage at the right end of the 20 k resistor. As an inverter, v b = Where v b is the voltage at the right end of the 50k resistor. As a summer v 0 = = [6 - 15] = 9V

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